Corrosion-resistant alloy



CORROSION -REESTAN T ALLOY John W. Graham, Ligonier, Pa., assignor to Kennametal Ino, Latrobe, Pa., a corporation of Pennsylvania No Drawing. Application May 2, 1955 Serial No. 505,541

13 Claims. (Cl. 29182.7)

My invention relates to an improved corrosion-resistant alloy and has to do, more particularly, with improvements in the corrosion-resistant hard composition of matter described and claimed in'the pending application for United States Letters Patent of Philip M. McKenna, Alex G. McKenna and John C. Redmond, Serial No. 268,004, filed January 24, 1952, as a continuation-in-part of an earlier application, Serial No. 74,742, filed February 5, 1949, and with improvements in the corrosionresistant hard composition of matter described and claimed in the application for United States Letters Patent of John C. Redmond and John W. Graham, Serial No. 313,810, filed October 8, 1952, issued June 21, 1955, as Patent No. 2,711,009.

The main object of my invention is to provide an alloy having properties or characteristics rendering it particularly suitable for use under conditions in which the material is exposed to corroding or oxidizing gases, at relatively high temperatures, such as for use for parts of jet propulsion motors, turbine buckets for gas turbines, parts for hot air engines, and parts for all sorts of industrial equipment, which require high strength and high oxidation resistance at elevated temperature. In other words, I propose to provide a novel alloy which is relatively light, but strong at elevated temperatures, and which is highly resistant to oxidation or corrosion at elevated temperatures.

A principal object of my invention is to provide an alloy which, with the low density and high resistance to oxidation of the compositions of said pending applications, will have a greater strength at high temperatures.

A primary method of evaluation of compositions or alloys, such as those disclosed in said pending applications, has been evolved and is called the stress-rupture test. It consists of maintaining a static tensile load on a suitable specimen at some specified elevated temperature until the specimen fails by breaking in tension in some interval of time between one and lO-hours. By testing a series of specimens at various loads, and at one temperature, a graph can be drawn with timethe abscissa and stress as the ordinate. The tests are generally made at several temperatures to develop a range of stress-temperature conditions. Various alloys are comparedby comparing the graphs. The results of the stress-rupture tests are expressed in terms of the stress required to rupture the specimen in 100 hours at a given high temperature, referred to as 100 hour stress to rupture strength. A further object of my present invention is to provide an alloy which is relatively light, strong and has high resistance to oxidation at elevated temperatures, and which also has a higher 100 hour stress to rupture strength.

A further object of my invention is to provide a sintered alloy having increased tensile strength, and which retains it at high temperatures.

A further object of my invention is to provide an alloy having superior high temperature strength, that is, which will retain its strength for a longer period at high temperatures, as compared with presently known materials used, for instance, for jet engine buckets.

Further objects, and objects relating to details and economies of operation, will appear more definitely from the detailed description to follow.

2,867,033 Patented Jan. 6, 1959 In general, my invention consists in substituting, for the nickel, cobalt or iron binder metal used in the compositions of said McKenna, McKenna and Redmond application, Serial No. 268,004, a binder metal consisting of an alloy of nickel, molybdenum and aluminum. The binder metal alloy should constitute from 20% to 70% of the composition, the nickel should constitute from 65% to by weight of the binder metal alloy, the molybdenum should constitute at least 2% of the binder metal alloy and aluminum should constitute from 3% to 25% of said binder metal alloy.

Before describing specific embodiments of my invention l will describe briefly the ways in which resistance to oxidation, transverse rupture strength, and hour stress to rupture value were measured to determine the characteristics of these specimens.

Resistance to oxidation or corrosion was measured by exposing surfaceground specimen test blanks, of like dimensions, in air, to a temperature of 1800 F., while resting on edge in ceramic combustion boats. Specimens were withdrawn, cooled, examined and measuredfor increase in thickness every 18 hours. Those specimens which passed through the complete test of 11 cycles (198 hours) with no more than .003 inch of adherent oxide growth per face were rated as Grade A (excellent). Those specimens which had, at the completion of the 11 cycles, an adherent oxide growth per face of between .003 inchand .008 inch were rated as Grade B. Those specimens which disintegrated into powder within the first 18 hour cycle were rated as Grade E (failure), and specimens having an oxide growth for 198 hours greater than .008 inch per face, but which did not disintegrate, were rated relatively as Grades C and D.

Values for transverse rupture strength were determined, by customary procedure, upon specimens .200 inch x .375 inch and with a span of .5625 inch between supports.

The stress-rupture test, used in obtaining the values given herein, consists of maintaining a static tensile load on a suitable specimen, at some specified elevated temperature, until the specimen fails by breaking in tension in some interval of time such as 100 hours. In this case, thespecimens were round rods of .156 inch diameter and about six inches long, ground to dimensions on a centerless grinder. By testing aseries ofspecimens at various loads and at one temperature a graph can be drawn. with time the abscissa and stress as the ordinate. The tests weremade at several temperatures to develop a range of stress-temperature conditions. The 100 hour stress to rupture value is obtained by noting the stress value at the intersection of the 100 hour abscissa with the graph.

The following are specific examples of alloys made in accordance with my invention.

The. titanium carbide used in this, and the following examples, was substantially devoid. of free titanium, free carbon, oxides. and nitrides and prepared by the method described and claimed in United States Letters Patent No. 2,515,463 of Philip M. McKenna, patented July 18, 1950. I have found it convenient to add columbium carcentimeter, a hardness of 86.0 on the Rockwell A scale,

a transverse rupture strength at room temperature of 1 208,000 p. s. i. (pounds per square inch), and a 100 hour stress to rupture value at 1600 F. of 40,500 p. s. i. and at 1800" F. of 15,000 p. s. i. This alloy showed excellent resistance to oxidation at 1800 F, the specimen being graded A on the scale of oxidation resistance above described.

Example 2 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 44.55

1 CbC 4.92 TaC 0.49 Ni 35.0

The alloy made from the mix above described, by the procedure hereinafter described, sintered at a temperature of 2700 F., had a density of 6.01 grams per cubic centimeter, a hardness of 85.9 on the Rockwell A scale, and a transverse rupture strength at room temperature of 150,000 p. s. i. The 100 hour stress to rupture value at 1600 F. was 32,000 p. s. i. and at 1800 F. was 10,500 p. s. i. The specimen showed good resistance to oxidation at high temperatures.

Example 3 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 52.75 CbC 4.15 TaC 3.04 Ni 27.0 Mo 10.2 -Al 2.8

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature of 2800" F., had a density of 6.66 grams per cubic centimeter, a hardness on the Rockwell A scale of 84.9, and a transverse rupture strength of 187,000 p. s. i. at room temperature. The 100 hour stress to rupture value of the specimen was 39,000 p. s. i. at 1600 F. and 16,000 p. s. i. at 1800" F. This specimen showed excellent resistance to oxidation at high temperatures, it having been rated Grade A on the scale above mentioned.

Example 5 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminumin the following proportions by weight:

Percent TiC 74.55 CbC 4.92 TaC 0.49 Ni 13.5

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature of 2700 F., had a density of 6.28 grams per cubic centimeter, a hardness of 89.2 on the Rockwell A scale, a transverse rupture strength at room temperature of 182,500 p. s. i., and the 100 hour stress to rupture value was'43,600 p. s. i. at 1600 F., 18,000 p. s. i. at 1800 F., and 3,700 p s. i. at 2000 F. The speciment showed excellent resistance to oxidation at high temperature, it being rated as Grade A on the scale above described.

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature of 2850 F., had a density of 5.60 grams per cubic centimeter, a hardness of 91.7 on the Rockwell'A scale, and a transverse rupture strength at room temperature of 124,000 p. s. i. The hour stress to rupture value of this alloy at 1800 F. was 26,000 p. s. i. and at 2000 F. was 2,900 p. s. i. A specimen of this alloy showed excel lent resistance to oxidation at high temperature, it having been rated Grade A on the scale described above.

Example 6 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight;

Percent TiC 54.55 CbC 4.92

TaC 0.49

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature of 2600 F., had a density of 5.99 grams per cubic centimeter, a hardness of 89.1 on the Rockwell A scale,

' and a transverse rupture strength at room temperature of 171,000 p. s. i. The 100 hour stress to rupture value of this'alloy at 1600 F. was 44,500 p. s. i. and at 1800 F. was 17,500 p. s. i. It showed excellent resistance to oxidation at high temperature having been rated Grade A on the scale above described.

Example 7 V This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature Q? 2400* ha a ensi y 03 6.-4.5 grams Per cubic r6611" timeter, a hardness of 82.0 on the Rockwell Ascale, and a transverse rupture strength of 261,000 p. s. i. at room temperature. The 100 hour stress to rupture value for this alloy was 18,000 p. s. i. at 1600" F. and 7000 p. .s. i. at 1800 F. A specimen of this alloy showed good resistance to oxidation at high temperature, it having been rated Grade B on the scale above mentioned.

Example 8 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

The alloy made from the mix above specified, by the procedure hereinafter described, sintered at a temperature of 2700 F had adcnsity of 6.40 grams per cubic Qntirncten a hardness of 86.6 on the Rockwell A scale, and a transverse rupture strength at room temperature of 189,000 p. s. i. A specimen of this alloy had a 100 hour stress to rupture value of 42,000 p. s. i. at 1.600? F. and 15,500 p. s. i. at 1800 F. Thisalloy showed excellent resistance to oxidation at high temperatures, having been rated Grade A on the scale above mentioned.

Example 9 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum andaluminum in the following proportions by weight:

The alloy made from the mix above specified, bythe procedure hereinafter described, sinter'ed at a temperature of 2650 F., had a density of 5.89 grams per cubic centimeter, a hardness of 90.7 on the Rockwell A scale,

and a. transverse rupture strengthat room. temperature of.146,000 p. s. i. The 100 hour to stress rupture value wa s,19,000 p. s. i. at 1800 F. and 3,800 p. s. i. at 2000 F. Thisalloy showed good resistance to oxidationat high temperatures.

Example '10 This alloy consisted of titanium carbide,.columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

The alloy made from the mix above specified, bythe procedure hereinafter described, sintered at a temperature of 2700 F., had a density of 5.98 grams per cubic centi- .meter, a hardness of 91.0 on the Rockwell A scale and atransverserupture strength of 78,000. p. s. i. at room temperature. It showed good resistance to oxidation at 6 high temperatures, having been rated 'Grade- Ben the scale above mentioned.

Example 11 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 64.37 CbC 4.92 TaC 0.49

Ni 21.0 Mo 7 4.5 A1 4.5

A The alloy-made as-above specified, by the procedure hereinafterdescribed, sintered at a-temperature of 2850 F., had a density of 5.48 grams per cubic centimeter, a hardness of 87.3 on the Rockwell A scale, and a transverse rupture strength at room temperature of 95,000

p. s. r.

7 Example 12 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 54.55 CbC 4.92

TaC 0.49

Ni 28.0 Mo 6.0 A1 6.0

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2500 F., had a density of 5.85 grams per cubic centimeter, a hardness of 87.2 on the Rockwell A scale and a transverse rupture strength at room temperature of 152,000

p. s. i.

Example 13 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following, proportions by weight:

Percent TiC 46.37 CbC 2.08 TaC 1.52

Ni 35.0 Mo 4.0

The alloy made as above specified by the procedure hereinafter described, sintered at a temperature of 2800" F., had a density of 6.02 grams per cubic centimeter, a hardness of 85.1 on the Rockwell A scale and a transverse rupture strength at room temperature of 108,000 p. s. i. This alloy showed excellent resistance to oxidation at high temperatures, having been-rated Grade A on the scale above mentioned.

Example 14 This alloy consisted of titaniumcarbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 42.75 CbC 4.15

TaC 3.04 Ni 35.0 Mo 4.0 A1 11.0

The alloy made as above specified, by the" procedure hereinafter described, sintered ata temperature of 2700 F.,'had a density of 6.12 grams per cubi centimeter, a hardness of 84.8 on the Rockwell A scale, and a transverse rupture strength at room temperature of 126,000 1). s. i. This alloy showed excellent resistance to oxidation at high temperature, having been rated Grade A on the scale above mentioned.

Example 15 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

TiC 44.55 CbC- 4.92 TaC 0.49 Ni 37.5

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2700 F., had a density of 6.35 grams per cubic centimeter, a hardness of 85.7 on the Rockwell A scale and a transverse rupture strength at room temperature of 177,000 p. s, i. The alloy showed excellent resistance to oxidation at high temperature, having been rated Grade A on the scale above mentioned.

Example 16 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions byweight:

Percent Tic 47.09 CbC 2.63 Taf 0.26 Ni 3 5.0 M 7 .5 Al 7.5

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2750 F., had a density of 5.91 grams per cubic centimeter, a hardness of 84.2 on the Rockwell A scale and a transverse rupture strength at room temperature of 167,000 p. s. i. It showed good resistance to oxidation at high temperature, having been rated Grade B on the scale above mentioned.

Erample 17 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 44.55 CbC 4.92 TaC 0.49 Ni 33.8 Mo 12.7 3.5

The alloy made as above described, by the procedure hereinafter described, sintered at a temperature of 2750 F., had a density of 6.39 grams per cubic centimeter, a hardness of 86.1 on the Rockwell A scale and a transverse rupture strength at room temperature of 235,000

Example 18 This all-0y consisted of'titaniurn carbide, columbium Percent 'carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent Ti( 47 .09 CbC 2.63 Ta 0.26 Ni 46.0 Mn 2.0 A1 2.0

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2500 F., had a density of 6.38 grams per cubic centimeter, a

' hardness of 81.7 on the Rockwell A scale, and a transverse rupture strength at room temperature of 212,000

' p. s.i.

Example 19 I This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and alun iiruirn. ll the foflowing proportions by weight:

Percent TIP 44.55 Cb 4.92 TaP 0.49

' Ni 38.75 M 7 .5 A1 3.75

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2500 F., had a density of 6.43 grams per cubic centimeter, a hardness of 86.2 on the Rockwell A scale and a transverse rupture strength at room temperature of 210,000

Example 20 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and alummum 1n the following proportions by weight:

Percent 37.09 CbC 2.63 a 0.26 42.0 9.0 Al 4 9.0

Example 21 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent i 37.09 Cb 2.63 Ta 0.26 N 42.0 M 9.0 A1 9.0

The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2800 F., had a. density of 6.2 grams per cubic centimeter, a

hardness of 84.2 on the Rockwell A scale, and'a transverse rupture. strength of 186,000 p. s. i.

Example 22 This alloy consisted of titanium,carbide,. columbium carbide, tantalum carbide, nickel, molybdenum and aluminum in the following proportions by weight:

Percent TiC 27.09 CbC 2.63 TaC 0.26 Ni 49.0 Mo 10.5 Al 10.5

The alloy made as above specified, by the procedure hereinafter described, sinteredat a temperatureof 2600 F., had a density of 6.41 grams per cubic centimeter, a hardness of 81.1 on the Rockwell A scale, and a transverse rupture strength at room temperature of 200,000 p. s. 1.

Example 23 This alloy consisted of titanium carbide, columbium carbide, tantalum carbide, nickel, molybdenum and alu- The alloy made as above specified, by the procedure hereinafter described, sintered at a temperature of 2500 F., had a density of 7.04 grams per cubic centimeter, a hardness of 83.0 on the Rockwell A scale, and a transverse rupture strength at room temperature of 212,000 p. s. i. The 100 hour stress to rupture value for this alloy was 33,000 p. s. i. at 1600 F. and 14,000 p. s. i. at 1800 F. This was a strong alloy but its resistance to oxidation was not so great as most of the samples above mentioned, since it was rated Grade D on the oxidation resistance scale However, a similar alloy not containing the carbide phase had no resistance to oxida tion at high temperatures, since it disintegrated to a powder in the first eighteen hours of the test.

The alloys above described may be made by the method usually used for making cemented carbide compositions except that certain refinements are desirable for producing best results. The carbide constituents of the composition in the form of crystals passing through a sieve having 100 meshes to the inch, and the powdered auxiliary metal (nickel, molybdenum and aluminum) having an average particle size of about 25 microns are charged into a steel ball mill. The balls used in the mill may be either cemented carbide or steel since the presence of iron in these compositions is not deleterious. The ball mill is then filled with a light petroleum solvent to exclude the air therefrom and is thereupon sealed and the charge is ball milled for from three to six days, at the end of which time the liquid in the mill and charge is removed by decantation and evaporation and a temporary binder, such as 0.25 to 1.00% of parafiin is incorporated with the material. The average particle size of the material at the end of the ball-milling operation is from 1 to 5 microns. The mixture is next pressed to the desired shape or as near to it as feasible. Although this may be done by any conventional pressing method, I have found that much more desirable results are obtained by the use of the explosive pressing process described and claimed in U. S. Patent No. 2,648,125, granted August 11, 1953, for Explosive Pressing of Powdered Compositions. According to this process, pressure is applied to the material hydrostatically and rapidly from all directions and very high pressures may be so applied. After pressing the mixture to the desired form the pieces may thereupon. be sintered or theymay be further shaped by. machining operations and then sintered. However, if any very complex shape is required the material in this form has insulficient strength to withstand the necessary machining operations and in that case it is given a preliminary heat treatment at temperatures-of from 1900 to 2100.? F. to give it sufficient strength to withstand the pressure ofimachiningorworking with diamond tools, but such heat treatment is not sufficient to affect the sintering. After final shaping in which proper allowance must be made for shrinkage during sintering amounting to from 16 to 20% the final sintering is carried out at temperatures of from 2400 to 3000 F. in an electric induction furnace, in which a vacuum of 100 microns'or less is maintained throughout the sintering operation. After the cooling of the furnace, the pieces may be removed therefrom and brought to final shape as may be required by grinding with a diamond wheel, or by other means.

It is my belief that, at the sintering temperatures employed, the nickel, molybdenum and aluminum alloy so that the metal binding the carbide particles of the composition together is an alloy of nickel, molybdenum and aluminum.

I am aware that the alloys herein described are susceptible of considerable variation from the specific proportions given without departing from the spirit of my invention and, therefore, I claim my invention broadly as indicated by the appended claims.

Having thus described my invention, what I claim as new and useful and desire to secure by United States Letters Patent, is:

1. A corrosion-resistant alloy characterized by a density of from 5.4 to 7.1 grams per cubic centimeter, high resist ance to oxidation at temperatures of 1800 F. and above, high transverse rupture strength and a high stress-torupture value at elevated temperatures consisting essentially of a carbide phase sintered with a binder and which alloy is comprised of at least 30% of the carbide phase and at least 20% of the binder, said carbide phase in cluding titanium carbide (TiC) and at least 2% of columbium carbide (CbC) and said binder including at least 1.4% of aluminum, at least 13.5% nickel, and at least 2% of molybdenum.

2. The alloy of claim 1 in which the columbium carbide content is between 2% and 5% by weight of the composition.

3. The alloy of claim 2 in which the binder metal alloy constitutes from 20% to 70% by weight of the composition.

4. The alloy of claim 3 in which nickel constitutes from 65% to by weight of the binder metal alloy.

5. The alloy of claim 4 in which aluminum constitutes from 3% to 25% by weight of the binder metal alloy.

6. The alloy of claim 5 in which molybdenum constitutes from 3% to 30% by weight of the binder metal alloy.

7. The alloy of claim 6 in which the columbium car bide content is between 4% and 5% by weight of the composition.

8. The alloy of claim 7 in which the titanium carbide content is between 34% and 75% by weight of the composition.

9. The alloy of claim 8 containing approximately 42.75% titanium carbide (TiC), 4.15% columbium carbide (CbC), 33.8% nickel (Ni), 12.7% molybdenum (Mo), and 3.5% aluminum (Al), the balance being tantalum carbide (TaC).

10. The alloy of claim 8 containing approximately 44.55% titanium carbide (TiC), 4.92% columbium carbide (CbC), 35% nickel (Ni), 7.5% molybdenum (Mo), and 7.5% aluminum (Al), the balance being tantalum carbide (TaC).

.,..- l-L'The :alloy. of claim. 8 containing approximately 62.75% titanium carbide (TiC), 4.15% columbium car- ..-,-bide- (CbC), 27% nickel (Ni), 10.2% molybdenum Mo and 2.8% aluminum (Al), the balance being tan- :talum carbide (TaC) 12. The alloy of claim 8 containing approximately 34.55% of titanium carbide (TiC), 4.92% columbium carbide (CbC), 40.5% nickel (Ni), 15.2% molybdenum is (Mo), and 4.3% aluminum (Al), the balance being tant'alurn carbide (TaC).

References Cited in the filev of this patent UNITED STATES PATENTS Schwarzkropf Nov. 14, 1939 Redmond June 21, 1955 

1. A CORROSION-RESISTANT ALLOY CHARACTERIZED BY A DENSITY OF FROM 5.4 TO 7.1 GRAMS PER CUBIC CENTIMETER, HIGH RESISTANCE TO OXIDATION AT TEMPERATURES OF 1800* F. AND ABOVE, HIGH TRANSVERSE RUPTURE STRENGTH AND A HIGH STRESS-TORUPTURE VALUE AT ELEVATED TEMPERATURES CONSISTING ESSENTIALLY OF A CARBIDE PHASE SINTERED WITH A BINDER AND WHICH ALLOY IS COMPRISED OF AT LEAST 30% OF THE CARBIDE PHASE AND AT LEAST 20% OF THE BINDER, SAID CARBIDE PHASE INCLUDING TITANIUM CARBIDE (TIC) AND AT LEAST 2% OF COLUMBIUM CARBIDE (CBC) AND SAID BINDER INCLUDING AT LEAST 1.4% OF ALUMINUM, AT LEAST 13.5% NICKEL, AND AT LEAST 2% OF MOLYBDENUM. 